Magnesium-base alloy



United States Patent 3,370,945 MAGNESIUM-BASE ALLOY George S. Foerster,Midland, and John B. Clark, Detroit, Mich., assignors to The DowChemical Company, Midland, Micln, a corporation of Delaware No Drawing.Filed June 28, 1965, Ser. No. 467,771 6 Claims. (Cl. 75168) ABSTRACT OFTHE DISCLOSURE This invention relates to a magnesium base alloy freefrom zinc and containing aluminum, manganese and calcium and havingprimarily the following composition:

Alloying constituent: Weight percent Aluminum 0.l-l.75 Manganese 0.1-1.0Calcium 0.05-0.6

Balance, commercially pure magnesium.

Commercially pure magnesium is the purity grade metal as produced inelectrolytic cells.

The alloy of the invention exhibits excellent compressive yield strengthand is weldable without stressrelief. Furthermore, the alloy exhibitsgood resistance to creep; it is readily workable and it is relativelyinexpensive.

The binary magnesium base alloys containing aluminum are improved by theaddition of manganese, i.e., they exhibit better strength properties andimproved corrosion resistance. Now it has been found that the ternarymagnesium base alloys containing certain proportions of aluminum andmanganese are further improved by the addition of small amounts ofcalcium in the range of 0.05 to 0.6 percent by weight. The calcium andaluminum contents of the alloy can be varied to obtain variouscombinations of desirable properties. The alloy free from zinc additionsexhibits desirable characteristics of Weldability, castability androllability not found in the zinc containing alloy. Commercially puremagnesium normally contains trace amounts of zinc. Incidental inclusionof zinc as an impurity from all sources should not exceed about 0.03percent by weight of the total alloy.

There are two basic types of combination. The combination containinghigh calcium, in the range of about 0.3 percent by weight, and lowaluminum, e.g., about 0.5 percent by weight, exhibits good ageability,high strength and excellent creep properties. Such alloy is mostsuitable Where the alloy is arbitrarily not to be brought to final shapeor form by a cold working process, such as rolling, and high strengthmust be obtained by aging. Aluminum to calcium ratios in suchcombinations are less than about 2.6.

The other type combination contains low calcium in the range of about0.15 percent by weight and high aluminum, e.g., about 1.2 percent byweight. This combination. offers higher ductility, and bettercastability, weldability without stress-relief, and good workability.Such alloy is most suitable where the alloy is to be cold worked wherebyoptimum strength is developed. Aluminum to'calcium ratios in suchcombinations are greater than about 2.6 and the sum of the percent ofaluminum 3,370,945 Patented F eb. 27, 1958 ICC plus the sum of thepercent of calcium is less than about 2.2 percent.

Increasing the calcium content beyond about 0.3 percent results in analloy having better creep resistance and compressive yield strength, butgenerally results in poorer extrudability. However, more calcium may beused to advantage at higher aluminum levels for the purposes ofpreparing die castings and rolled sheet within the scope of theinvention.

Manganese contents above about 1 percent impair properties, causesegregation, and tend to coarsen the cast grain structure. The alloycontaining a manganese content below about 0.1 percent does not exhibitdesired strength levels. Preferably the manganese content is in therange of 0.3 to about 0.8 percent.

Preferably the present alloy composition contains, by weight, from about0.25 to abuot 1.5 percent of aluminum, from about 0.3 to about 0.8percent of manganese, and from about 0.1 to about 0.4 percent ofcalcium, the balance being substantially commercially pure magnesium(purity about 99.8 percent).

Two especially preferred alloys have the following compositions, byWeight: 1) 0.5 percent of aluminum, 0.75 percent of manganese, 0.3percent of calcium, and the balance magnesium, and (2) 1.25 percent ofaluminuin', 0.50 percent of magnanese, 0.15 percent of calcium, and thebalance magnesium.

The alloy may be made in the desired proportions according to theinvention by melting together the alloy ingredients in properproportions or by using hardeners of magnesium alloys containing thealloy constituents. In addition, the manganese may be added by directreduction of manganese halide added to the flux.

Protection from oxidation during alloying is effected by the use of amagnesium chloride-free saline flux as in conventional alloying. Themolten alloy may be flux refined by stirring the alloy with additionalflux. The sorefined alloy is allowed to settle and may then be separatedfrom the flux as by decanting into a suitable casting mold, as forexample, a slab mold for rolling stock or a billet mold for extrusionstock. In the event the alloy is employed in die casting, theflux-refined metal may be decanted into the holding pot of the diecasting machine.

The present alloy exhibits better creep resistance than the frequentlyused commercial alloy having the ASTM designation AZ91B.

The molten alloy of the invention is normally cast into either rollingslabs or extrusion billets. Usually the external surface of the castpiece is removed, as by a scalping operation. Extrusion billets arepreheated to about 600-900 F. and are then die-expressed from a heatedcontainer. Rolling slabs are heated to about 700950 F. and reduced inthickness to about 0.1 inch sheet by multiple passes through the rollsof a mill, reheating the metal as necessary to avoid cracking.

The so-rolled metal sheet is then finished in a number of Ways asdesired. The rolled metal may be annealed one hour at a temperature inthe range of 700 to 950 F., quenched, and reduced by cold rolling at lto 2 percent per pass through steam heated rolls under conditions closeto the cracking limit, and further annealedat a temperature in the rangeof 300 to 700 F. This method is particularly applicable to the presentalloy having a relatively high aluminum to calcium weight ratio.

The rolled metal may also be finished by heating about one hour at 700to 950 F., warm rolling the sheet to final thickness in one pass throughthe rolls of the mill, the metal exciting from the rolls at atemperature of 300 to 800 F., and quenching the exciting metal. Ifdesired, the quenched metal may be aged or annealed at a temperature inthe range of 300 to 800 F.

The alloy of the invention exhibiting a relatively low aluminum tocalcium weight ratio is desirably and conveniently finished withoutfurther rolling upon solution heat treating the rolled metal at atemperature in the range of about 850 to 950 F., after which the metalis immediately quenched, and thereafter aged at a temperature of about300 to 350 F.

Examples To illustrate the advantageous results which can be Car apurities, preheated to 600900 F. and ram extruded conventionally througha die while the metal and the container were at temperatures in therange of 500-800 F. Each alloy was extruded into a inch x inch strip attwo different extrusion speeds, namely, 20 feet per minute, and a speedin the range of '70100 feet per minute. The so-obtained extrusions wereaged 24 hours at 350 F. to bring the metal to the T5 temper conditionand the extrusions were then subjected to mechanical testing. Theresults of these tests are shown in Table II.

achieved by the present invention, a series of composin TABLE IIProperties, Extrusion at Composition, Percent by Weight 1 Test No. Al/Ca20 fpm, 100 f.p.m.

Al Ca Mn Percent E CYS TS Percent E CYS TS 3 0. 17 0. 6 1. 8 12 16 37 1215 39 0 3 0. 34 0. 6 0. 9 14 18 36 15 17 37 0. 0. 54 0. 6 0. 6 14 20 36Hot short 0. 5 0. 2 0. 6 2. 5 8 15 40 16 40 0. 5 0 3 0. (5 1. 7 10 17 4010 19 39 1. 0 0. 54 0. ti 1. 9 14 26 40 Hot short 1. 0 0.20 0. ti 5. 011 17 40 11 18 40 1.0 0. 13 0. 3 7. 2 10 39 11 15 39 1 Balancecommercial purity magnesium. 2 Metal cracked on being extruded.I.p.m.=feet per minute.

tions according to the invention were prepared and cast into respectiverolling slabs (e.g., 2" x 4" x 8" Each slab was treated as follows: thefaces of the slabs were scalped to remove surface impurities orinclusions, the slab was heated to 700950 F. and reduced in thickness toabout 0.1 inch sheet by multiple passes through the ro1ls of a mill,reheating the metal as necessary to avoid cracking. The rolled metal wasthen either annealed one hour at 950 F. and quenched, or, annealed forone hour at 700 F. Some of this metal was brought to a hard tempercondition by cold rolling, at 1 to 2 percent per pass through steamheated rolls under conditions close to the cracking limit, and furtherannealing (one hour at 300 F). Some of the cold rolled metal was broughtto the soft temper condition by annealing at 700 F., for one hour,instead of at 300 F. The s0-obtained metal in each of the hard temperand soft temper conditions was tested to determine the physicalproperties of the sheet. The results are listed in Tabie I.

In an additional test series, compositions according to the inventionwere prepared and cast both as extrusion stock and rolling stock.Extrusion stock was scalped and heated to a temperature in the range600900 F. and extruded into inch x inch strip at 700 F. from a 3-inchcontainer at a rate of from about to about 100 feet per minute. Theso-obtained strip was aged 24 hours at 350 F.

Rolling stock was scalped and heated to a temperature in the range700-950 F., then hot rolled starting with an initial temperature of 850F., being reduced in thickness, by multiple passes through the rolls ofa mill, from 2 inch to 0.1 inch. The so-obtained sheet was solution heattreated one hour at 950 F., water quenched and aged 24 hours at 320 F.

TABLE I Composition, Percent Physical Properties Test by Weight 1 AnnealNo. Temp, Hard Temper Soft Temper Creep 2 at 300 F.,

I 5,000 p.s.i., 100 hrs., Al Ca Mn Percent E CYS TS Percent E CYS TSpercent extension Additional compositions according to the inventionwere each prepare d and cast as a 3-inch diameter extrusion sheet werbillet. Each billet was scalped to remove surface im- CY S=cornpressionyield strength in 1000's of pounds per square inch TS=ultirnate tensilestrength in 1000's of pounds per square inch.

The so-obtained extrusion strip and these-obtained e each subjected tomechanical testing. The results of these tests are shown in Table III.

TABLE III T t N Composition, Percent by Weight 1 Properties, Extrusionat 50 f.p.m. Properties, Rolled Sheet Al Ca Mn Percent E CYS TS PercentE CYS TS 0. 5 0. 3 0. 25 14 10 34 lb 21 38. 5 0. 5 0. 3 0. 5 12 20 39 122 30, 5 0.5 0. 3 1. 0 12 19 3E) 10 20 38 1 Balance commercial puritymagnesium.

metal was subjected to mechanical testing. The results 5 of these testsare shown in Table IV.

about 0.5 percent by Weight of aluminum, from 0.3 to about 0.8 percentby Weight of manganese, about 0.3 percent by Weight of calcium, and thebalance substantially magnesium [free from zinc], the Weight ratio ofaluminum to calcium being less than about 2.6 percent, and the alloybeing characterized by good ageability without cold working.

TABLE IV Physical Properties Test Composition, Percent by Weight 1Anneal, N0. Temp. F. Hard Temper Soft Temper Al Cu Mn Percent E OYS TSPercent E CYS TS 15 l. 0. 13 0. 3 700 26 36 16 14 35 1.0 0.13 0. 3 900 231 41 16 17 34 1.6 1. 0 0. 20 0.6 700 3 25 36 19 34 17 1. 0 0. 31 0. 6700 3 26 37 19 15 3 1 1 Balance commercial purity magnesium.

Among the advantages of the alloy of the invention are that the alloypossesses the characteristic lightness of magnesium and the simultaneouscombination of weldability without stress-relief, strength, workability,and low cost.

We claim:

1. The magnesium base alloy consisting essentially of from 0.1 to 1.75percent by Weight of aluminum, from 0.1 to 1.0 percent by weight ofmanganese, from 0.05 to 0.6 percent by weight of calcium, and thebalance substantially magnesium [free from Zinc], the combined totalamount or aluminum and calcium in the alloy not exceeding 2.2 percent byweight.

2. The magnesium base alloy, as in claim 1, in which the Weight ratio ofthe aluminum content to the calcium content is less than about 2.6percent.

3. The alloy, as in claim 1, in which the weight ratio of the aluminumcontent to the calcium content is greater than about 2.6 percent.

4. The magnesium base alloy consisting essentially of from 0.25 to about1.5 percent by weight of aluminum, from 0.3 to about 0.8 percent byweight of manganese, from 0.1 to about 0.4- percent by weight ofcalcium, and the balance being substantially magnesium [free from zinc].

5. The magnesium base alloy consisting essentially of 6. The magnesiumbase alloy consisting essentially of 1.2 percent by weight of aluminum,from 0.3 to 0.8 percent by weight of manganese, about 0.15 percent byweight of calcium, and the balance substantially magnesium [free fromzinc], the weight ratio of calcium to aluminum being greater than about2.6 percent, and the alloy being characterized by weldability withoutstressrelief and by good cold workability.

References Cited CHARLES N. LOVELL, Primary Examiner.

